This invention relates to the production of trialumialuminum nickelide fibers. More particularly, this invention concerns itself with a leaching process for removing trialuminum nickelide fibers from a two-phase, composite, aluminum/trialuminum nickelide matrix.
The inclusion of a controlled eutectic alloy of trialuminum nickelide within an aluminum body has proven to be an effective means for providing tensile strength enhancement in aluminum bodies. The trialuminum nickelide filaments are generally grown within the aluminum body as an aligned microstructure in the form of whiskers or filaments. In addition to providing enhanced tensile strength in aluminum bodies, the whiskers of aluminum nickelide also find use in a variety of industrial and military microelectronic applications, provided they can be removed from the aluminum-trialuminum nickelide matrix in an undamaged condition.
A number of methods are presently known for producing aluminum nickelide whiskers in an aluminum matrix. The principal method utilizes a unidirectional solidification technique. Another method involves the growth of aluminum nickelide fiber bundles longitudinally in a rod-shaped aluminum matrix. Still other methods are well known and even newer methods are contemplated since a considerable research effort is being conducted in an attempt to develop even more efficient means of growing these useful fibers. Unfortunately, a fundamental problem exists in the removal and separation of these fiber materials from the two-phase, solid matrix within which they are grown. Therefore, an important need exists for the development of an efficient, practical and simple method for removing the nickelide fibers from the matrix in order to study their effectiveness for various microelectronic applications as well as evaluate the effectiveness of new production procedures which may be conceived of in the future. Also, another problem exists in that the usefulness of these fibers for various microelectronic applications is severely limited unless a method or system can be developed for their removal from the matrix without damage to the fibers. The difficulties encountered in separating the fibers from the solid matrix are due to the similar properties displayed by both the nickelide fibers and the aluminum in the matrix itself. Heretofore, the various separation methods have utilized acid leaching and electrolytic procedures for separating the fiber material. Unfortunately, these prior art methods involved many drawbacks. The acid-leaching procedure had to be precisely timed and the yield proved to be quite low. The electrolytic method required expensive equipment and electricity. Other methods were accompanied by gas evolution resulting in bird-nesting of the fiber bundles as they were exposed. Also, when using aqueous acid etches, a low selectivity of attack constituted a problem since the aluminum nickelide fibers, as well as the bulk aluminum matrix itself, were often dissolved. It became obvious, therefore, that a system which could effect the facile separation of the trialuminum nickelide fibers without damage from the bulk aluminum phase would circumvent the problems encountered in using prior art methods of separation.
After a considerable research effort, the problem of providing an efficient and effective means of separating trialuminum nickelide fibers filaments from a two-phase, composite matrix of aluminum and trialuminum nickelide have been solved by the process of this invention. The aluminum nickelide fibers are separated in extremely good condition using inexpensive chemicals and ambient conditions. In general, the process consists of dissolving the composite matrix with a solution containing oxalic acid and hydrogen chloride.